The present invention relates to a disk array apparatus provided, through communicable connection with a host computer and/or another disk array apparatus not allowed for direct connection with the host computer, for storage of data coming from the host computer into a storage region derived by adding together a storage region of another disk array apparatus and a storage region of the disk array apparatus, and a control method for such a disk array apparatus. In the below, the disk array apparatus is referred to as storage control unit.
In database systems such as data centers and others handling large data, data management is performed using a storage system that is separately provided from a host computer (in the below, referred to as “host unit”). The storage system is exemplified for a disk array apparatus, in which a plurality of storage devices are arranged in an array. The disk array apparatus is configured based on RAID (Redundant Array of Independent Inexpensive Disks), for example. A set of such storage devices provides a physical storage region formed with at least one or more logical volumes (logical units) The logical volume is made available to the host unit, more specifically, to a data base program operating on the host unit (hereinafter, referred also to as “application program”). Through transmission of a predetermined command, the host unit can perform data writing/reading to/from the logical volumes.
In the rapidly advancing information society, data volume is increasing on a daily basis for database management. Such a data increase is fueling demand for a larger-capacity, higher-performance storage control unit, and to meet such a market demand, there have been developed storage control units of an advanced type. Installation of the advanced-type storage control unit into the storage system may be done in two manners: one is the manner of totally replacing a previous-type unit(s) with an advanced-type unit(s), and thereby, configuring the storage system from the beginning (JP-A-10-508967). The other is the manner of newly adding an advanced-type unit(s) to the storage system configured only by a previous-type unit(s) to use both types therein.
Also known is a technology of dynamically configuring a logical device on a sector basis through management of storage region of a physical device also on a sector basis (JP-A-2001-337850).
To configure a logical device from a plurality of storage devices varying in capacity, applied is a technology of using the storage device having the smallest capacity as a reference for area formation to other remaining storage devices (JP-A-9-288547).
The issue here is that the data communications performance becomes sometimes poor between a host unit and a storage control unit provided externally thereto. This is caused due to poor connection therebetween specifically when an application program on the host unit makes an attempt to acquire inquiry information from the external storage control unit. Further, at the time of acquisition of the inquiry information, such a connection failure between the host unit and the external storage control unit may prevent the application program from supporting the inquiry information in the external storage control unit.
Similarly, when (an application program of) a host unit and (that of) another host unit provided externally to an internal storage control unit connected to the host unit make an attempt to acquire inquiry information from an external storage control unit, the external storage control unit may be structurally incapable of responding to a (remote copy) command coming from the external host unit.
There may be a case where an internal storage control unit performs a remote copy following a copy command issued thereto from (an application program of) a host unit. The remote copy may be made from a storage device of a remote-copy-incapable external storage control unit to a virtual device provided in the internal storage control unit. There may also be a case, together with such a remote copy, where the internal storage control unit performs copy from its storage device to a virtual device. During such copy, if the directly-connected external host unit makes access to the external storage control unit, the copy details are disadvantageously corrupted thereby. This is because the external storage control unit is not able to reject access from the external host unit in such a case.